The use of a balun has been common for many years, and different designs are well known. It will be appreciated that a balun is a device which is used to couple a balanced impedance, such as an antenna, to an unbalanced transmission line, such as a coaxial cable. A balun prevents asymmetrical loading of the balanced impedance and the induction of currents on the exterior of the unbalanced transmission line.
In European Patent Application No. 0,474,490, there is disclosed an antenna arrangement which may be switched between dipole and monopole modes, the dipole and balun being provided as conducting areas on opposite sides of a printed circuit board, but the arrangement is far from compact, and the dipole lengths are provided by interconnected complex shapes.